The present invention relates generally to improvements in electrical devices intended for surface mounting on printed circuit boards and in the mounting components thereof.
Electrical devices adapted to be mounted to the surface of printed circuit boards are conventional. Circuit boards on which such electrical devices are surface mounted are provided with terminal pads or areas which form part of the printed circuits, and the devices are provided with contacts or leads having pad-engaging portions which are configured and positioned to be placed in overlying alignment with the terminal pads. Generally, the pads are coated with a solder paste composition and, after the pad-engaging contact portions are placed into engagement with appropriate terminal pads, the solder composition is reflowed to thereby obtain a secure electrical engagement between each contact portion and its respective terminal pad. Connector devices are also mechanically connected to the boards, generally by mounting posts that are inserted into corresponding openings formed in the board until their barbed or hooked ends snap into engagement with the underside of the board.
Since the terminal pads on the board are coplanar, it would be advantageous if the pad-engaging contact portions of the surface mounted device were also precisely coplanar so that all the contact portions could be placed into electrical engagement with the terminal pads without having to deflect or flex one or more of the contacts to bring the other contact portions into engagement with the terminal pads. However, this is not possible to accomplish on a production basis so that in practice, one or more of the contacts must be deflected to some extent in order to bring all the contact portions into electrical engagement with their corresponding terminal pads. The unavoidable deflection of one or more of the contacts in assembling a surface mounted device to a printed circuit board results in a biasing force being built into the assembly which tends to separate the device from the board and cause the integrity of the soldered electrical connections to degrade.
Moreover, conventional mounting posts used to mechanically connect devices to printed circuit boards present problems. In the case of surface mount applications, when the hooked ends of the mounting posts of a board-mounted device snaps into engagement with the underside of the board, the impact may cause hundreds of small components that are laying in the solder paste prior to the surface mount soldering process to be jarred from their pads. In both surface and pin mount applications, the mounting posts must be specially sized for each application, having an appropriate diameter corresponding to the diameter of the opening in the printed circuit board, and a length corresponding to the board thickness.